1. Field of the Invention
The present invention relates to a feedback controller, and specifically relates to a feedback controller which compensates for a delay time characteristic and a mechanical resonance characteristic of an object to be controlled or a detecting means, and thereby can stably control an amount to be controlled.
2. Description of the Prior Art
FIG. 1 is a configuration diagram of a general feedback control system, for example, as shown on page 2 of "University Lecture, Automatic Control" issued from Maruzen Co., Ltd. (written by Masami ITO). In FIG. 1, numeral 1 designates a reference input element in which an aimed value of control is an input signal and a reference input signal r being the output signal of this reference input element 1 is given to a comparator part 2 which compares the signal r with a main feedback signal y* as described later and outputs a control deviation e. The control deviation e of the comparator part 2 is given to an adjusting part 3 determining an amount of operation based thereon, and an output signal of the adjusting part 3 is given to an operating part 4 converting it into an amount of operation u of higher power. Then, a controlling part 5 having a transfer characteristic Gc1(s) is constituted with the adjusting part 3 and the operating part 4. The amount of operation u of the controlling part 5 is given to an object to be controlled 6 which has a transfer characteristic Gp(s).Gpn(s) and outputs an amount to be controlled y. The outputted amount to be controlled y is given to a detector part 7 which has a transfer characteristic Ks Gsn(s), converts the amount to be controlled y into an electric signal and outputs the main feedback signal y*. In addition, in the object to be controlled 6 and the detector part 7, the Gpn(s) and the Gsn(s) are deviations from desired characteristics of the object to be controlled 6 or the detector part 7 respectively, representing the mechanical resonance characteristic and the delay time characteristic.
The conventional feedback control system is constituted as mentioned above, and in performing the feedback control thereof, to make the amount to be controlled y agree with the aimed value, the amount to be controlled y is detected by the detector part 7 to be fed back to the comparator part 2, and a difference from the reference input signal r being an output of the reference input element 1 is calculated by the comparator part 2, and this calculated value is the control deviation e. In the controlling part 5, the amount of operation u is outputted to the object to be controlled 6 so that the control deviation e outputted from the comparator part 2 is brought close to zero. This means that the controlling part 5 operates as a stabilizing compensator for stabilizing a feedback loop system. In this feedback control system, a round transfer characteristic (open-loop characteristic) from the control deviation e to the main feed-back signal y* is as follows: EQU Go1(s)=Gc1(s).multidot.Gp(S)Gpn(s).multidot.Ks Gsn(s) (1)
The conventional feedback control system as mentioned above has problems as enumerated below.
(1) Normally, the object to be controlled 6 and the detector part 7 have always deviations from desired characteristics represented by Gpn(s) and Gsn(s) respectively in the high frequency band, and as is obvious from Equation (1), these Gpn(s) and Gsn(s) appear intact in the open-loop characteristic, therefore deteriorating the stability of the feedback control system. In general, the controlling part Gc1(s) is designed so that the gain of an open-loop characteristic Go1(s) is OdB in a relatively low frequency band wherein the system is not affected by Gpn(s) and Gsn(s), and therefore the band of the feedback control system cannot be extended, and the system is vulnerable to outside disturbance, and the control deviation e is likely to become large.
(2) When detection noise is mixed into the detector part 7, particularly, frequency components lower than the band where the detector part 7 operates are not eliminated at all and are fed back intact to the comparator part, and therefore the operation of the control system is likely to be disturbed by this noise.